Casting investment material and process



CROSS REFERENCE UNITED STATES PATENT OFFICE aosuss oss'rmc. mvss'rmm'r MATERIAL m. r raocsss Charles H. Prange, Lyndhurlt, N. 1., aslignor to Austenal Laboratories, Inc., New York, N. Y.. a corporation of New York No Drawing. Application April 20,1934, Serial No. 721,550

9 Claims. (01. 22-1 This invention relates to a new and improved casting investment material and process.

While the present casting investment material and process are particularly advantageous in the casting of high temperature fusing alloys, such as stainless steel and the like and the alloy more fully disclosed in my copending application Serial No. 599,071, filed March 15, 1932, it is to be understood that the investment material and proc- 10 es of the present invention are not limited to.

the casting of such alloys but may be employed in casting other materials as suitable or desired.

Furthermore, I shall describe the invention in )5 connection with mechanical dentistry, but it is to be understood that the invention may be used elsewhere as suitable or desired.

Heretofore, in the art, plaster of Paris (gypsum or calcium sulphate) has been the com- 20 mon mold or investment material used in mechanical dentistry. Its most valuable features are the property of easy handling by pouring the watery mixture and its subsequent prompt hardpending application above identified, plaster of Paris is not sufllciently refractory. It fluxes and decomposes andthe castings are not satisfactory due to rough surfaces, holes and sulphur contamination. Also, it has a tendency to shrink when the mold is presheated and to become very 4o fragile as a result of this heating which interferes with producing the requisite thermal expansion of the mold for compensation for casting shrinkage. In these molds, the function of the plaster of Paris has been that of a binder 45 for the filler or aggregate.

. Another method heretofore used for makin molds for high fusing castings is to use silicate of soda as a binder for the refractory aggregate. However, silicate of soda is strongly basic and readily acts as a flux to reduce the refractoriness of the mold. It, therefore, is not suitable for use with the most desirable aggregates having high thermal expansion such as silica. .As commonly used, it also has'no satisfactorily controllable setting qualities, but hardens principally by drying out.

The most successful dental mold material for high fusing castings was developed by the present applicant using organic silicates as the 5 binder for the refractory aggregate, as more fully disclosed in applicant's prior Patent No. 1,909,008 patented May 16, 1933, but this mold material has certain disadvantages due to rather com- I plicated handling and relatively high cost. m

The object of my present invention is to provide a mold material which will be highly refractory for casting high fusing metals and al-' loys, such as stainlesssteel and the like and the high fusing alloy of my copending application above identified, and which will not involve complicated handling or high cost.

Another object is to provide a mold material in which the requisite thermal expansion of the mold for compensation for casting shrinkage may be produced without any tendency to shrink when the mold is pre-heated, or to become fragile as a result of such heating.

Another object is to provide a mold material for casting high fusing alloys without fiuxing or decomposition, also without sulphur contamination and without producing rough surfaces or holes in the castings.

I accomplish the foregoing and such other objects as will hereinafter appear by mixing a relatively large percentage of an aggregate of high thermal expansion with a relatively small percentage of a setting binder and compacting the mixture by vibration to bring the particles into contact and to produce a hard and relatively non-shrinking mold.

Any material which is highly refractory or of highthermal expansion, such as silica, may be used as the filler or aggregate. This aggregate is preferably of graded fineness, from about eighty mesh to about ten microns, particle size, with a part of the fine dust under ten microns removed.

EXAMIN 2 I a,os1,sss

mina, are decidedly refractory, and, at the same time, retain the valuable hydraulic setting characteristics of Portland cement and plaster of Paris. I mix with the refractory aggregate 5 just enough of the aluminous cement to serve as a'binder, and I find that an amount comparable to the amount of fine dust which is removed will serve that purpose. when combined with a suitable refractory aggregate, such as previously described, these aluminous cements will resist temperatures of at least 2500 F.

An illustrative example of a suitable aluminous cement for the purpose of this invention is the cement known in the art as "Lumnite" cement made by the Atlas Lumnite Cement Company. These aluminous cements are much faster setting than ordinary Portland cement, but are still very slow setting compared to plaster of Paris, requiring about twelve hours to set completely.

It. is to be understood that binders other than aluminous cement may be employed within the scope of the present invention. For example, magnesium oxide and magnesium chloride, or magnesium oxide and zinc chloride may be employed as a binder for the graded refractory aggregate of silica.

For the purpose of accelerating the setting of the composition, I add a small amount of setting accelerator. This setting accelerator may be lime, gypsum, ordinary plaster, plaster of Paris, Alpha gypsum (known in the art as Hydrocal", and made by the United States Gypsum Company), or any other suitable setting accelerator. And instead of adding a setting accelerator, the

setting of the present material may be accelerated by the application of heat within the scope of my present invention. By the application of heat, the material may be set in less than one hour.-

I have found a mixture having the following composition suitable for purposes of the present invention:

' Ounces Silica, or other aggregate of high thermal pansion, of graded fineness, from approximately eighty mesh to approximately ten microns, particle size, with a part of the fine dust under ten microns removed 20 Aluminous cement 3 Setting accelerator while the constituents of the above composition are given by weight, it will be understood that the relative weights give the relative proportions in one illustrative mixture and that these proportions may be followed with other quantities of the constituents to provide a larger or smaller, but at least somewhat similarly proportioned mass.

- In making up the mold or mold part, water is added to the foregoing composition in an amount to bring the composition to the desired consistency. After the composition is thus brought to the desired consistency, it is molded or shaped into whatever form is desired in the final product, and in molding or shaping the material, it is compacted by vibration to bring the particles into contact and to produce a hard and relatively-non-shrinking mass. The compacting of 70 the mixture by vibration may be accomplished as by means of a suitable revolving cam which will raise the mixture slowly and drop it abruptly, thereby compacting theparticles into contact without agitating the mixture. The partic- 75 ular manner of compacting the mixture to obtain the desired results and without agitating the same may be accomplished in any other suitable or preferred manner. In the case of a revolving cam, a speed of 100 R. P. M. is suitable' for purposes of the present invention, although 6 that, too, may vary within the scope of the appended claims.

The foregoing composition will set hard in about two to three hours, and, by the control of the relative particle size of the silica content, the 10 mixture may be compacted to bring the particles into contact and to produce a hard and relatively nonshrinking mass. Shrinkage, upon drying out and upon heating, is thus avoided, and a strong, hard, refractory mass is produced with 15 a smaller percentage of binder than would be required if the mixture were designed to be merely poured and allowed to harden like plaster of Paris. Furthermore, a maximum silica content is provided so that when a dental mold or mold 20 part, or other mold or mold part, .is made, a high degree of thermal expansion is obtainable by heating the mold prior to casting so that casting shrinkage can be adequately compensated for. I am further enabled to reduce the setting 25 accelerator to the least possible proportion to avoid any appreciable reduction in the refractory value of the material if and where that seems desirable. The setting time may be varied by changing the proportion of setting accelerator, 30 and the hardness of the refractory mass may be increased or decreased by varying the amount of aluminous cement or other binder. The mass sets hard throughout.

Further mixtures suitable for purposes of th 35 present invention are as follows:

Silica, eighty mesh and finer ounces l8 Silica sand, approximately sixty mesh do 2' Aluminous cem do 3 Accelerator grams 2% and Silica, eighty mesh and finer ounces 18 Silica, four hundred mesh do 2 45 Aluminous cement (in 3 Accelerator a "gram... l

and

Silica, eighty mesh and finer ..ounoes 20 Aluminous cement.- do 6 Accelerator .grams.. 2%

The first of the above three compositions will pack in about twenty-five minutes and will set in about four hours, whereas the second compo- 55 sition will pack in about thirty-five minutes and set in about three hours, and the last of these compositions will pack in about ninety minutes and set in about two hours. The manner of making up the mold or mold part and the manner 60 of compacting the mixture to bring the particles into contact and to produce a hard and relatively non-shrinking mass may be substantially as described in connection with the first composition set out in the present. application. 65

I have found that the quantities of the constituents of the present material may vary within the scope of the present invention. For example, I have used the aluminous cement in the proportions of six ounces maximum to one ounce minimum in relation to twenty ounces of silica. And the accelerator has been varied from one gram minimum to nine grams maximum.

The present materials are also adapted for use as a coating for the surface or surfaces of a suitable mold base. In such cases the mixed investment material maybe ied intoanair jet at great speed. or other mechanical means, and this air jet or other means will spray and depos'itthe 5 material over thedesired The particles will be compacted into contact by vibration, in thesenseinwhichthlstermisusedintheappendedclaimainmuchthemannerinwhich the -tionmaybeputwlllbelargely'ohvioustothose skilled in the art. The invention is, oi course,

20 admirably suitable for making the ordinary oi mold or investment which conforms to the accurate and unique contours and confirmations oi 7 models supplied by the dentist ior the purpose oicasting in the mold cavitya denture or applie :5 shoe which is adapted ultimately to ac-' curatelytothe originalmodel. Anditis adapted for industrial uses and elsewhere as suitable or" desired.

'lhe present inventionis not limited to the par- 3 ticular details herein described. All equivalent constitutents and all equivalent steps in the process are intended to-iallwithin the scope oi the appended claims.

I claim: 5 1. The method oi iorming a casting mold which comprises mixing a refractory assr sate oi around silica oi selected grain size from about eighty mesh to about ten microns particle size and in amount to form the body oi the mold with apartoithefinedustundertenmicronsin amount equal to approximately irom 13% to 23% by weight oi the total weight 01' the mixture removed and replaced with a binder oi aluminous cement in amount to serve as a binder for the aggregate and hydraulically to set the mixture, the silica aggregate being in major proportion,

and an accelerator oi the class which includes plaster. plaster oi Paris, lime, gypsum and Alpha gypsum. and compacting the mixture to brine the 50 particles into contact and produce a and relatively non-shrinking mass.

2. A composition oi'matter combined in substantially-the proportions as follows:

- Y "Ouncm s5 Bilica.orother aggregateoihighthermalexpension. oi graded finenus, from awl' ximately eighty mesh to approximately ten s. a composition oi in sub- 7 the proportions as ioliows: 1

Silica. s ty meshand finer ouuces... l8

Sillcasand, approximatelys'ixtymesh.do 2 5 Aluminous cement. "do"-.. 8

Accelerator grams- 2% '4. A, composition of matter combined in substantially the proportions as iollows: m Silica, eighty mesh and finer -ounces.- 18 Silica. four hundred meslL; -.-do. 2 Aluminous cement -..do.. 3 Accelerator gram 1 5. A composition 01' matter combined in substantially the proportions as iollows:

Silica, eighty mesh and fiuer ..-..ounces 20 Alumlnous'cement; do.-- 8

6. The method oi forming a casting mold which 7 comprises particles 01 silica, removing a part oi the fine dust under ten microns therefrom in amount equal to approximately irom 13% to23%' by weight of the total weight oithe 25 mixture, and mixing the graded particles oi silica with a hydraulically setting binder similar to aluminous cement in amount hydraulically to set the mixture and substantially equal to the amount oi dust removed and with'a setting accelerator. f

7. The method oi forming acasting mold which comprises grading particles of silica. removing a part oi the fine dust under approximately ten microns thereirom'in amount equal to from approximately 5% to 23% by weight oi the total weight of the mixture, and mixing the graded particles oi silica with an hydraulically setting binder similar to aluminus cement in amount hydraulically to set the mixture and substantially equal to the amount of dust removed and with a 40 setting accelerator.

8. The method at forming an investment compound which comprises grading partlcles oi silica, removing a part of the fine dust under approximately ten microns thereirom' in amount equal to from approximately 5% to 23% by weight of the total ,weight oi the mixture. and the graded, particles of silica with an hydraulically setting" binder similar to aluminus cement in amount hydraulically to set the mixture and subsgntiallyequaltotheamountoidustremov p 9. The method of iormlng aninveatment compoundoitheclassdescrlbedandcapableoideii niteexpansion'by heat. which comprises mixing witli a refractory mote an moi-alumna setting binder similar to aluminus cement in amount equal to from approximately 8% to 23% by weight oi the total weight oi the mixture.

CHARLES H. PRANGI.

Accelerator -srams 

